The subject matter disclosed herein relates generally to isotope production systems, and more particularly to shielding of targets of the isotope production systems.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that has a magnet yoke that surrounds an acceleration chamber. The acceleration chamber may include opposing pole tops that are spaced apart from each other. Electrical and magnetic fields may be generated within the acceleration chamber to accelerate and guide charged particles along a spiral-like orbit between the poles. To produce the radioisotopes, the cyclotron forms a beam of the charged particles and directs the particle beam out of the acceleration chamber and toward a target system having a target material (also referred to as a starting material). The particle beam is incident upon the target material thereby generating radioisotopes.
During operation of an isotope production system, large amounts of radiation (i.e., unhealthy levels of radiation for individuals nearby) are typically generated within the target system and, separately, within the cyclotron. For example, with respect to the target system, radiation from neutrons and gamma rays may be generated when the beam is incident upon the target material. With respect to the cyclotron, ions within the acceleration chamber may collide with gas particles therein and become neutral particles that are no longer affected by the electrical and magnetic fields within the acceleration chamber. These neutral particles, in turn, may also collide with the walls of the acceleration chamber and produce secondary gamma radiation.
Thus, during production of radio isotopes, such as for Positron Emission Tomography (PET) applications, the starting material (confined in the target system) is typically irradiated with high energy particles. Accordingly, the target system and the materials used to construct the target system are also exposed to the high energy particles and will thus also be highly radioactive. The high radioactive activation of the target system makes servicing and handling of the equipment generally very time and cost consuming, in particular, because of the need to wait for acceptable radiation levels to decrease, which may take at least 24 hours. Even after this time period, precautions are necessary when approaching the system because radiation exposure levels are strictly regulated by law. Thus, servicing of this kind of equipment is also difficult as service personnel may quickly reach maximal annual limits. Accordingly, in order to reduce dose load per person, a relatively high number of people may be required to share the dose to reasonable levels.
To protect nearby individuals from the radiation (e.g., employees or patients of a hospital), isotope production systems may use shields to attenuate or block the radiation. In conventional isotope production systems, shielding of the radiation (e.g., radiation leakage) has been addressed by adding a large amount of shielding that surrounds both the cyclotron and the target system. However, the large amounts of shielding may be costly and too heavy for the rooms where the isotope production system are to be located. Alternatively or in addition to the large amounts of shielding, isotope production systems may be located within a specially designed room or rooms. For example, the cyclotron and the target system may be in separate rooms or have large walls separating the two.